Re: [xml] Beginner's question about xPath

[Kasimier Buchcik <kbuchcik 4commerce de>]

Hi,

On Thu, 2005-06-30 at 15:52 -0400, Liam R. E. Quin wrote:
> On Wed, 2005-06-29 at 15:39 -0400, ABeylin axsone com wrote:
>
> > I cannot figure out how to use xPath without loading the entire XML into
> > memory.
>
> This is an implementation-specific question, and for libxml2 the answer
> is usually that you will need the whole document in memory.
>
> If this is a problem (e.g. very large documents) there are other
> approaches, especially with XPath 2.0 -- XSLT 2.0 and XQuery which both
> use XPath 2.0 can operate over indexed collections of documents,
> although there are not yet many implementations of that feature, and
> none I think using libxml2.
>
> The problem is that XPath expressions can easily be written that rely
> on the entire document, e.g. count(//*) or section[position() = last()]
> or using the ancestor axis to navigate around.  A lot of research has
> been done on optimising XPath, some of it in the database community,
> especially in conjunction with XQuery (www.w3.org/XML/Query).
>
> Hope this helps although it might not be very encouraging!
>
> Liam

For people eager to dive into implementing streaming XPath for Libxml2:
I found [1], a Java implementation for a subset of XPath, including
predicates, to be quite informative for me. But just googling for
"streaming XPath" will get you there anyway...

[1] http://www.cs.umd.edu/projects/xsq/

Regards,

Kasimier